Hi Mark. Looking at your pix, I see that you have the same "altered" system on your 68 that I had on my 69 when I bought it. It will never work correctly that way.

You have a pressure cap on the radiator. The hose runs from the "radiator pressure overflow" to the expansion tank. Water can flow only when the pressure of the cap on the radiator is exceeded, i.e. boiling over. I had NOTHING but trouble with this rigged up system.

I bought a correct copper/brass radiator, without the cap. The water then flows directly to the expansion tank without having to overcome the pressure cap on the radiator. My BB runs at 180-200 even on the hottest of days, and I've put thousands of miles on it over the past 3 years.

There are/were many variations in the radiator usage, BB, SB, With AC, Without AC, etc. IF your application originally used a radiator with its' own radiator cap, your car did not originally use a "surge" or expansion tank. If your car originally used a radiator without a cap, then your car originally used the surge tank. AC cars used the long copper/brass "tube" shaped surge tank. That's the real expensive one. :) Chuck


[Modified by Chuck Gongloff, 3:41 AM 10/3/2003]

 

I just recently fitted one of these stainless steel units and have it fitted in front of the radiator and mounted to the radiator support frame. Looks good, does the job and cleans up the engine bay even more.

 

Chuck offers excellent advice.

Perhaps to clarify this discussion, the following is a summary of the three strategies GM used on Corvettes:

1) Radiator with built in expansion tank, and no overflow/collector tank

GM built millions of vehicles like this, including Corvettes. The poster's vehicle was originally equipped this way. The expansion tank was integral to the radiator, and requires that the radiator NOT be to be filled to the top to operate properly. If it is overfilled, the excess will always be puked overboard. Pointless and unneccessary to keep refilling it.

2) Radiator with external expansion tank, no overflow/collector tank.

Many early C3 and C2 Corvettes came equipped this way. Due to construction/space requirements, the expansion tank mentioned in case 1) above was moved to an external tank, usually seen as the aluminum Harrison tank on the right fender well and connected in line with the heater hoses. This is a pressurized vessel operating at the same pressure as the rest of the system controlled by the radiator cap. If it is overfilled, the excess will always be puked overboard. Pointless and unneccessary to keep refilling it.

3) No expansion tank external or internal, but external overflow/collector tank

This is how all '73 and up Corvettes are configured, and how the original poster has been operating his car with the Buick tank.

Excess fluid is expelled from the radiator to the tank as required, and also reinducted as required. NOT a pressurized vessel and vented to atmosphere. Not mounted inline with the heater hose. If it is overfilled, the excess will always be puked overboard. Pointless and unneccessary to keep refilling it.

The key to understanding system 1) is that if overfilled, it is guaranteed that it will puke. It is not a sign of malfunction or overheating. There MUST be a few inches of air space at the top to allow for expansion. The system will puke any excess until proper balance is established. If the car overheats with the radiator at the correct level, it's not a design defect or can be fixed by overfilling it. Find the root cause. System 2) operates the same way, and almost all C2 and C3 owners go through the learning curve of puke/fill/puke/fill/puke till they learn to let the system find it's own level.

System 3) is what we're all used to on modern cars, and what the original poster converted his car to.

What's going on with this post is the idea using a system 2) expansion tank, but as a system 3) overflow/collector tank.

I can understand converting the car to a system 3) but not using a system 2) tank.

Hope this helps.

:cheers:

 

Chuck, Allow me to quote myself, from above:

Imagine my horror when I learned that one of the few "correctly dated" parts on my car was not supposed to be there at all!!!! :eek: I will probably remove it at some point. I certainly won't change the radiator to match the expansion tank. It does not rely on that top hose to feed it from the radiator's pressure cap. It gets a flow of coolant from the heater hoses. And of course I am not recommending that anyone install one of these things where it doesn't belong. My only recommendation is to catch and recirculate any overflow rather than allowing it to dump to the street, using a plastic bottle, milk bottle, coke can, or one of those snazzy metal aftermarket catch-cans like Brutus has :) .

Mike, Are you giving GM too much credit by describing system #1 as having an internal expansion tank? My understanding is the 3" I leave at the top of the radiator is the space for expansion. If GM considers that an "internal tank", so be it. Otherwise, your explanations should clear things up for everyone. If there are still any questions, I would be happy to continue beating this topic to death!! :lol: MJ


[Modified by MNJack, 1:07 PM 10/3/2003]

 

I wasn't trying to give GM credit for inventing it, this was the universal standard configuration used on ALL automobiles (domestic and foreign) probably going back to the earliest horseless carriage.

Yes, the 3" of space at the top is the 'internal expansion tank'. :D